This cooling-channel piston has an upper part and a lower part, wherein these two parts are connected to each other by way of a cohesive joint, specifically friction welding. After being joined, these two parts form an annular, circumferential cooling channel that is located approximately behind a ring belt. As an option, the cooling-channel piston can have a cooling chamber, transfer passages between cooling channel and cooling chamber, as well as cooling pockets. No cooling chamber, no transfer passage and no cooling pockets are required in order to implement the teaching of this document.
Friction welding of upper part and lower part is particularly preferred. Other methods of joining or connecting, such as electron beam welding, bonding, clamping, bolting or similar can also be applied.
A cooling-channel piston is known from WO 2006/034862 A1 that consists of an upper part and a lower part. These two parts are permanently attached using a friction welded joint. An annular cooling channel is formed by the upper part and the lower part (can also be formed by only one of the parts) and is located approximately behind a ring belt.
The ring belt terminates in the upper part (facing/towards/) the lower part in a circumferential ring wall that can be supported via a gap geometry on a matching abutting/contact surface of the lower part, which is also circumferential.
In this prior art a corresponding gap geometry is shown in FIGS. 1 to 4.
Using this gap geometry, it must be ensured during operation of the cooling-channel piston in the internal combustion engine that the outer area of the upper part below the ring belt is supported on the corresponding upward facing area of the lower part, in particular in the skirt area. At the same time, it must be ensured with this gap geometry that the cooling medium present in the annular cooling channel during operation of the cooling-channel piston in the internal combustion engine, which is being circulated and exchanged, does not escape by way of this gap geometry.
These gap geometries, however, as described in WO 2006/034862 A1, have significant disadvantages.
The part of the gap area that extends in the direction of the annular cooling channel can no longer be checked and no longer be reworked/refinished if upper part and lower part are joined permanently to each other, in particular when employing friction welding. This area is no longer accessible following the joining process. If it should turn out that, as a result of manufacturing (or even possibly during operation of the cooling-channel piston), this gap area or even the entire gap area is too small, the upper part bears on the lower part when loaded under the force of gas pressure. As a result stresses are created that can result in cracks forming in the connecting joint, in particular the friction weld joint. If, on the other hand, the gap is too large, the cooling medium can force its way outwards in undesirable amounts through this gap towards the cylinder wall.